A dive watch is known in the prior art that comprises a case, which bears a pressure sensor comprising a membrane and a transmission device. The membrane is capable of deforming mechanically under the effect of external pressure to then act on the transmission device. This device thus transmits said deformation movement representing the pressure in order to be amplified, for example, so that the pressure value detected by the sensor is displayed.
In general, the membrane of this sensor is made from crystalline material such as e.g. an alloy composed of copper and beryllium (Cu—Be).
Every material is characterised by its Young's modulus E, also called elasticity modulus (generally expressed in GPa), which characterises its resistance to deformation. Moreover, every material is also characterised by its elastic limit σe (generally expressed in GPa), which represents the stress beyond which the material will plastically deform. Thus, it is possible, for a given thickness, to compare materials by establishing for each one the ratio of their elastic limit to their Young's modulus σe/E, wherein said ratio is representative of the elastic deformation of each material. Therefore, the higher this ratio is, the greater the elastic deformation of the material. Crystalline materials such as those used in the prior art, e.g. the alloy Cu—Be, which has a Young's modulus E equal to 130 GPa and an elastic limit σe that typically amounts to 1 GPa, give a low σe/E ratio, i.e. in the order of 0.007. These crystalline alloy membranes therefore have a limited elastic deformation. In the case of the membrane of a pressure sensor, this means a limited measurement range.
Moreover, because this elastic limit is low, when it deforms the membrane approaches its region of plastic deformation under low stresses with the risk that it cannot resume its initial form. To avoid such a deformation, the deformation of the membrane is restricted, i.e. the amplitude of the movement of the membrane is intentionally limited. It is then understood that the transmission movement must be amplified. This results in noise that is detrimental to the pressure sensor and, moreover, to the display of the pressure value.
In addition, the use of precious crystalline metals for the production of such a pressure sensor membrane, or any other active element of a timepiece, is not conceivable considering the inadequate mechanical characteristics of these metals. In fact, these precious metals in particular have a low elastic limit in the order of 0.5 GPa in the case of alloys of Au, Pt, Pd and Ag, as opposed to about 1 GPA in the case of the crystalline alloys classically used in the production of pressure membranes. In view of the elasticity modulus of these precious metals, which is in the order of 120 GPa, a σe/E ratio of about 0.004 is obtained. However, a high σe/E ratio is necessary for the production of such a membrane, as explained above.
Consequently, the person skilled in the art is not encouraged to use these precious metals for the production of such a membrane.